This invention concerns a method for managing the operating conditions of an anti-theft security device for a motor vehicle (automotive vehicle, motorcycle or lorry), such device being of the type comprising—portable transmitting means,—receiving means on board the vehicle and—means controlling at least one system for interrupting at least one circuit required for operating said vehicle (engine ignition circuit, fuel intake circuit or other . . . ) when the distance between the transmitting means and the receiving means exceeds a certain value. This invention also concerns the anti-theft security device enabling the implementation of the method.
It is known by the document EP-0 319 428 a security device for automotive vehicle, comprising a portable transmitter which transmits a high frequency signal (HF), and a fixed receiver adapted for interrupting automatically the engine ignition circuit of the vehicle when the distance between said portable transmitter and said on-board receiver exceeds a certain value. Such a system enables to stop the motorisation of the vehicle, particularly in case of theft, as soon as said vehicle moves away from the carrier of the transmitter.
The transmitter sends a low power, encoded cyclic signal HF. When this signal is acknowledged and validated by the receiving means, a relay or equivalent closes the engine ignition circuit for its operation. When the receiving system no longer receives the transmitted signal HF, the relay interrupts the ignition circuit to stop the motorisation.
Time delay means have been provided to maintain the control of the relay for a duration greater than the duration between two encoded sequences, in order to avoid any abusive interruption in case of transients, or more generally in case of accidental signal loss.
However, if the duration of accidental loss of this signal is greater than the time delay duration, the ignition circuit is automatically interrupted by means of the relay and the motorisation of the vehicle does not operate any longer. In case when it happens whereas the vehicle is in use, the driver may have a tendency to control the lever or the accelerator, and when the signal is reset, sudden return to service of the motorisation may cause said vehicle to become incontrollable.
The purpose of this invention is to remedy this shortcoming.